Carbide Wear Surface and Method of Manufacture

ABSTRACT

A radial bearing having a wear surface with improved wear characteristics comprises a steel support, to which is bonded a metal carbide composite wear surface made by first arranging, within a cavity defined between a steel mold and the steel support, tiles made of microwave sintered, cemented metal carbide, closely packing the voids between the tiles with metal carbide powder, and infiltrating the mold cavity with a metal brazing alloy by subjecting the filled mold to rapid heating. The brazing alloy fills voids between the metal carbide particles, the microwave sintered metal carbide tiles, and the metal support, thereby relatively rapidly consolidating the carbide into a wear layer bonded with the steel support without substantially damaging the properties of the microwave-sintered metal carbide tiles.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/866,953 filed Sep. 26, 2015, which is a divisional of U.S. patentapplication Ser. No. 13/351,300 filed Jan. 17, 2012, the entirety ofwhich is hereby incorporated by reference.

BACKGROUND

Tools used in connection with drilling of oil and gas wells are subjectto considerable abrasion and wear during use. For example,mud-lubricated radial bearings used as drill bits, rock mills, mudmotors, are subject to highly abrasive particles found in drillingfluids and frequently require replacement. Metal carbides, particularlytungsten carbide (WC), are used to form a bearing or wear surface fordownhole tools because of their desirable properties of hardness,toughness and wear resistance. There are a number of different methodsfor applying tungsten carbide to a substrate or support to form a wearsurface for a bearing.

Conforma Clad®, a brazed tungsten carbide cladding, sold by Kennametal,is one example of a tungsten carbide wear surface that can be used forbearings. Examples of commercially available products with ConformaClad® wear surfaces include radial bearings used in downhole mud motors.These tungsten carbide clad surfaces are fabricated by overlaying asurface of an object to be clad to form a wear surface with a clothcontaining tungsten carbide powder, mixed with a binder, and then layingon top of it another cloth containing a braze alloy before subjectingthe part to heating to melt the binder phase and the braze.

Another method, described in U.S. Pat. No. 4,719,076, uses a blend ofmacro-crystalline tungsten carbide powder and cemented tungsten carbidecobalt chips to create a hard wear surface on a radial bearing. Themixture described in U.S. Pat. No. 4,719,076 is comprised of sixtypercent by weight of 80 mesh macro-crystalline tungsten carbide,commercially available as the Kennametal product called P-90, and fortypercent by weight of cemented tungsten carbide cobalt crushed chips witha mesh size of 10/18. The percentage of weight of tungsten carbidecobalt chips is from forty to eighty percent by weight. To create abearing surface, a steel blank is surrounded by a graphite mold and theblended mixture of macro-crystalline tungsten carbide and cementedtungsten carbide chips is loaded into a cavity created between the steelblank and graphite mold. After the mold contents are vibrated to achievemaximum density of the blended mixture tungsten powder, copper basedinfiltrant is then placed in a funnel shaped ring formed around the topof the mold. The mold is then heated to 2050 degrees Fahrenheit, plus orminus 25 degrees Fahrenheit, by induction heating, causing the copperinfiltrant to melt and infiltrate the heated powder mixture in thecavity through capillary action. Once infiltrated, it is slowly cooledto room temperature. After cooling, the parts are machined to specificdimensions by grinding.

Cemented tungsten carbide is one example of a hard composite materialfabricated by mixing together a powder formed of particles of a carbideof one of the group IVB, VB, or VIB metals, with a metal binder inpowdered form, pressing the mixture into a desired shape to form a“green part,” and then sintering the green part to cause the binder tomelt and thereby form an agglomeration of carbide particles bondedtogether by the metal binder phase. The binder material is typicallycomprised predominantly of cobalt, nickel, or iron, and alloys of them.The most common example of a cemented metal carbide composite used indownhole applications is tungsten carbide (WC) with a cobalt binder.

Microwave sintering of metal carbides with a metal alloy as a catalystor binder phase material is described in several patents, including U.S.Pat. Nos. 6,004,505, 6,512,216, 6,610,241, 6,805,835, all of which areincorporated herein by reference. In a microwave sintering process,loose grains of metal carbide, which constitute a metal carbide powder,and a metal binder powder are combined to form an homogenous mixture,which is then shaped or formed into a “green” part that has very nearthe dimensions and shape of a desired cemented metal carbide part. Thegreen part is formed, for example, by compacting the carbide and binderpowders into a mold by cold pressing. It may also be precast with asacrificial wax if necessary. One example of a metal carbide is tungstencarbide. The metal binder that is typically used is a metal alloycontaining about 80 to 100 percent cobalt. Additional materials can alsobe added to the mixture. The green part is then sintered using microwaveradiation to heat the part to a point that is below the meltingtemperature of the metal carbide, but high enough to cause the metalbinder to melt throughout the matrix of metal carbide grains, resultingin the particles of carbide fusing or adhering to one another to therebyform a single, solid mass. Microwave heating shortens sintering times.Shorter sintering times result in less chemical and phase change in themetal binder, which is typically cobalt or an alloy containing cobalt.More even heating is also possible, which results in more uniformshrinkage of the part and more uniform distribution of the binder duringcooling. Shorter sintering times also result in smaller changes in thesize of the grains. Smaller changes in the grain size result in morepredictable and consistent carbide grain structures. Microwave sinteringalso allows for uniform cooling after sintering, which allows for bettermanagement of stresses within the part and better phase control of themetal binder. A microwave sintered metal carbide part typicallypossesses higher modulus of elasticity, yield strength, and impactstrength and greater thermal and electric conductivity as compared to apart having the same starting materials sintered using conventionalHP/HT and HIP methods.

SUMMARY

An article having a wear surface with improved wear characteristicscomprises, in one example, a steel support to which is bonded a metalcarbide composite wear surface made by first arranging, within a cavitydefined between a mold and the steel support, tiles made of cementedmetal carbide, closely packing the voids between the tiles withspherical metal carbide powder, and infiltrating the mold cavity with ametal brazing alloy by subjecting the filled mold to rapid heating. Inone embodiment, the heating lasts for a period of less than one hour.The brazing alloy fills voids between the spherical metal carbideparticles, the cemented metal carbide tiles, and the metal support,thereby relatively rapidly consolidating the metal carbide into a wearlayer bonded with the steel support without substantially damaging theproperties of the microwave sintered metal carbide tiles. The mold isremoved by machining or grinding it away, exposing the wear surface,which then is machined and polished to desired dimensions.

In one exemplary embodiment, the mold is made of steel for enabling morerapid and even heating using an induction furnace.

A radial bearing of this type, made with tiles of microwave sinteredtungsten carbide cemented with cobalt, and using a brazing alloycontaining copper (Cu), nickel (Ni) , and manganese (Mn), can havesubstantially improved wear characteristics as compared, for example, toone with a wear surface made from a Conforma Clad tungsten carbidecladding. Subjecting the mold to less than one hour of heating helps topreserve the properties of the microwave sintered tungsten carbide tilesby reducing diffusion of cobalt from the tiles into the brazing alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart representing certain steps of an exemplaryprocess for manufacturing a radial bearing have a metal carbide wearsurface.

FIGS. 2A, 2B and 2C are, respectively, perspective, top andcross-section views of a first example of a radial bearing madeaccording to the method of FIG. 1.

FIGS. 3A, 3B, and 3C are, respectively, perspective, top andcross-section views of a second example of a radial bearing madeaccording to the method of FIG. 1.

FIGS. 4A and 4B are, respectively, perspective and top views of anexample of the inner radial bearing shown in FIGS. 2A-2C, with a wearsurface made according to the method of FIG. 1, and FIG. 4C is a crosssection of FIG. 4B taken along section line 4C-4C.

FIGS. 5A and 5B are, respectively, perspective and top views of anassembly of a mold and mandrel for making the inner bearing shown inFIGS. 4A-4C, and FIG. 5C is a cross section of FIG. 5B taken alongsection line 5C-5C.

FIGS. 6A and 6B are, respectively, perspective and top views of theexample of an inner radial bearing shown in FIGS. 3A-3C, with a wearsurface made according to the method of FIG. 1, and FIG. 6C is a crosssection of FIG. 6B taken along section line 6C-6C.

FIGS. 7A is a top view of an assembly of a mold and mandrel for makingthe inner bearing shown in FIGS. 6A-6C, and FIG. 7B is a cross sectionof FIG. 7A taken along section line 7B-7B.

FIGS. 8A and 8B are, respectively, perspective and top views of theexample of an outer radial bearing with a wear surface shown in FIGS.2A-2C and made according to the method of FIG. 1, and FIG. 8C is a crosssection of FIG. 8B taken along section line 8C-8C.

FIGS. 9A and 9B are, respectively, perspective, and top views of anassembly of a mold and mandrel for making the inner bearing shown inFIGS. 8A-8C, and FIG. 9C is a cross section of FIG. 9B taken alongsection line 9C-9C

FIGS. 10A and 10B are, respectively, perspective and top views of theexample of an outer radial bearing shown in FIGS. 3A-3C, with a wearsurface made according to the method of FIG. 1, and FIG. 10C is a crosssection of FIG. 10B taken along section line 10C-10C.

FIGS. 11A and 11B are, respectively, perspective and top views of anassembly of a mold and mandrel for making the outer radial shown inFIGS. 10A-10C, and FIG. 11C is a cross section of FIG. 11B taken alongsection line 11C-11C.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the following description, like numbers refer to like elements.

FIG. 1 describes a process 100 for fabricating a part of a radialbearing suitable for a downhole application. Although the process isparticularly advantageous for fabricating a radial bearing havingenhanced durability for downhole applications, it could be adapted forfabricating wear surfaces on other objects. Examples include bearingsand wear surfaces in construction, mining, or other equipment that havepotential to expose a bearing or wear surface to abrasive materials.FIGS. 2A-2C and 3A-3C illustrate two variants of one example of asemi-finished, two-piece, radial bearing suitable for a downholeapplication. The process will be described with reference to theseradial bearings.

Referring to FIGS. 2A-2C, radial bearing 200 includes an inner bearing202 and an outer bearing 204. Just the outer bearing 204 is capable ofbeing used as a journal for a shaft, in downhole applications. However,with drilling fluid being used as a lubricant and coolant in suchapplications, having wear layers on both surfaces will tend to reducetimes between failures. The inner bearing is connected with a rotatingshaft and the outer bearing is mounted within a housing or other elementof the downhole tool. The outer diameter, or outer surface, of innerbearing 202 has applied to it a carbide wear layer 206 using process100. Similarly, the inner diameter or surface of outer bearing 204 hasapplied to it a carbide wear layer 208 using process 100. Carbide layer206 forms an outer wear surface for the inner bearing, and carbide layer208 constitutes an inner wear surface for the outer bearing. Microwavesintered metal carbide tiles 210 can be seen arranged in aclosely-spaced relationship within each wear layer, with the volumebetween each of the tiles filled in with infiltrated, spherical metalcarbide powder.

Radial bearing 300 of FIGS. 3A to 3C is another example. It has an innerbearing 302 and an outer bearing 304. The outer diameter or surface ofthe inner bearing has applied to it a carbide wear layer 306, and theinner diameter of the outer bearing has applied to it a carbide wearlayer 308. One difference, as compared to radial bearing 200 (FIGS.2A-2C), is that the inner bearing 302 and the outer bearing 206 eachinclude a lip 310 and 312, respectively, at each end that overhangs therespective carbide layers 306 and 308.

Referring back to FIG. 1, a first part of the exemplary process 100involves placing tiles of a microwave sintered, metal carbide compositematerial in a closely spaced arrangement on a steel mandrel—acylindrically shaped body—as a first step to forming a wear surface fora radial bearing. In one, preferred example, the tiles are microwavesintered tungsten carbide that is cemented using a cobalt alloy.However, other metals can be used as binders, including iron, nickel,and alloys of them. The mandrel forms or comprises a support componentfor the carbide wear layers for either the inner or outer radial bearingand, as such, acts as a substrate for the carbide wear layer. An outerbearing is formed on the inner diameter of a hollow mandrel. An innerbearing is formed on the outer diameter of a cylindrical mandrel, whichmay or may not be hollow. The mandrel used to form the inner bearing ismade from a smaller diameter mandrel.

These tiles are made by forming a green part containing a mixture ofmetal carbide powder and a binder into the shape of the tile, andrapidly heating it using microwave radiation, thereby sintering thegreen part to form a tile made of microwave sintered tungsten carbide. Adescription of examples of such a process can be found in the patentsreferenced in the background, above. One example of the metal carbidepowder is tungsten carbide powder and one example is a cobalt alloypowder.

The tiles of microwave sintered metal carbide are made relatively thinand wide. They are, in this example, also uniform in their shapedimensions with respect to each other. Each has a substantially circularshape, substantially the same diameter, and substantially the same,uniform thickness. “Substantially the same” means that it is withinacceptable manufacturing tolerances. Examples of diameters range from 5mm to 10 mm, with thickness ranging from 0.5 mm to 3 mm. A circularshape is common and comparatively easily fabricated with desiredmaterial characteristics. However, other shapes can be used.Furthermore, having tiles with a substantially uniform shape anddimensions provides certain advantages in manufacture and is acceptablefor radial bearings. However, tiles of more than one shape could beused, though uniform thickness is preferred. Optimum area and thicknessof the tiles are determined in part by the curvature of the surface onwhich they are being placed. The tiles could be formed with a curvedback and/or front surface that better approximate the curvature of thewear surface of the radial bearing.

At step 102, at least one row of cemented metal carbide tiles areaffixed or attached to a steel mandrel using, for example, a sacrificialadhesive to hold them in place. These tiles may be affixed in otherways. For an inner bearing, the tiles are affixed to the outer diameterof the mandrel, and for an outer bearing, they are affixed to the innerdiameter of a mandrel with a cylindrically shaped bore or hollow center.Step 102 is optional but helps to ensure correct arrangement of tilesthat are subsequently loaded into a cavity formed between the mandreland a mold by establishing a first row of tiles that are properly spacedand positioned, and that do not move. Once one or more initial rows oftiles are affixed, a mold is fit at step 104 onto the mandrel, so thatthe surface of the mandrel on which the wear surface will be formedfaces the mold. For an inner radial bearing, the wear surface will beformed on the outer diameter of the mandrel, with the mold placed aroundthe mandrel. For an outer bearing, the wear surface will be formed onthe inner diameter of a mandrel with a hollow center or bore, with themold being placed inside the hollow center. The mold is dimensioned sothat a cavity is formed between the mold and the mandrel that isslightly greater than the thickness of the wear surface to be formed,the thickness of the cavity being just large enough to accommodate thetiles arranged around the surface of the mandrel that the mold faces.

Additional cemented metal carbide tiles are then loaded at step 106 intothe cavity by dropping them through a slot or opening at one end of thecavity, between the mold and mandrel. The tiles are generally loaded onerow at a time, with tiles in a row partially resting in the spacesbetween tiles in the row below. The result is a relatively uniformarrangement of closely spaced tiles. Some of the tiles abut one another.However, some space between the tiles may exist due to, for example,slight differences in dimensions in the tiles or a mandrel withcircumference that does not match the length of the row of abuttingtiles.

At step 108, metal carbide powder is loaded into the cavity. The metalcarbide powder is preferably spherical. Each granule or particle ofspherical metal carbide powder is, as compared to, conventionalmacro-crystalline carbide, generally spherical in shape. Granules ofmacro-crystalline tungsten carbide, such as Kennametal® P-90, haveshapes that are angular and irregular. The spherical metal carbidepowder is preferably tungsten carbide. “Spherical” granules arecomparatively much more round and uniformly shaped, but not perfectlyspherical or exactly alike. One example of spherical tungsten carbide isTEKMAT™ spherical cast tungsten carbide powder. It is preferred that themesh size of the powder is between 25 microns and 500 microns, as thosesizes result in a more durable wear surface. The mold is shaken to causethe powder to flow down and around the tiles so that it fills and iswell packed into the spaces or voids between the tiles.

A funnel in the slot or opening of the cavity is positioned at the topof the mold and mandrel assembly at the top of the circular slot. In oneexample, the funnel is integrally formed by the mold and the mandrel. Inanother example, it is a separate piece that is placed on top of theassembly of the mold and mandrel. If the funnel is in place on the topof the mold and mandrel assembly near the beginning of theprocess—either because it is integrally formed by the mold and mandrelor it is a separate piece that is placed there—the funnel can assistwith loading the metal carbide tiles and the metal carbide powder.However, it will be used primarily, if not entirely, for the purpose ofholding nuggets or chunks of braze material, as well as flux, that willbe used to infiltrate the tile and metal carbide powder matrix in thecavity of the mold.

As step 110, flux is added into the funnel at the top of the mold,followed by braze at step 112, and then more flux at step 114.

With the mold loaded with the cemented metal carbide tile and sphericalmetal carbide power, and the braze and flux loaded into the funnel, themold is loaded into a furnace for heating at step 116. In one examplethe furnace is comprised of an induction coil. An alternative example isthe molded bearing is placed in the center of the coil. Assuming thatcobalt cemented tungsten carbide tiles made by microwave sintering andspherical tungsten carbide powder are being used, the induction coil isoperated at step 118 to cause the mold to heat rapidly to approximately1900 degrees Fahrenheit (F) or 1000 degrees Celsius (C) in an airatmosphere. The heating causes the braze to melt and infiltrate thematrix of spherical metal carbide powder and microwave sintered,cemented metal carbide tiles through capillary action and gravity. Oneexample of a suitable braze is one made of nickel (Ni), copper (Cu), andmanganese (Mn). The heating is completed at step 120 without damagingthe properties of the steel mandrel or the metal carbide tiles. In theillustrated example, heating lasts less than an hour. By using a steelmold in addition to a steel mandrel, the induction heating is not onlymade more rapid, but also the resulting heating is more uniform. Byheating the molded part for no more than one hour, properties of themicrowave sintered tungsten carbide tiles tend not to be damaged andtheir integrity is better preserved. The shortened heating time forinfiltration of the braze reduces inter-diffusion between the cobaltfrom the tiles and the brazing alloy. As an alternate induction heating,microwave heating, using a microwave furnace, can be used to heat themold.

Once heating is stopped, the mold and mandrel assembly are cooleduniformly to a temperature of less than 100 degrees Celsius at step 122.The mold is then removed, at step 124, by machining, milling and/orgrinding it away. Once the mold is removed, exposing the wear surface,the wear surface is machined, ground and polished to a smooth surfacewith predetermined dimensions at step 126, thus resulting in a finishedbearing. During the finishing process, any braze on the surface of thetiles is removed, and the tiles are ground to give them a surfacecurvature.

FIGS. 4A-4C illustrate one example of an inner radial bearing 400 madewith the process described above, and FIGS. 5A-5C illustrate mold 500and mandrel 502 assembly for fabricating a wear surface on the innerradial bearing 400. Inner radial bearing 400 is substantially the sameas inner radial bearing 202 of FIG. 2. The inner radial bearing includesa cylindrical support 402, on which is formed a wear surface 404 madeaccording to process 100 of FIG. 1. The cylindrical support 402 is madefrom a section of mandrel 502, as indicated in FIG. 5C. Microwavesintered metal carbide tiles 406 form part of the wear layer matrix,along with spherical metal carbide, which surrounds the tiles. When mold500 is press fitted to mandrel 502, as shown in FIGS. 5A-5C, the mandreland mold cooperate to define a cylindrically shaped cavity 504 betweenthe mold and the section of the mandrel that will form the cylindricalsupport 402 for the bearing, as well as circular funnel 506 that feedsinto slot 508. The slot is an opening into cavity 502, through whichtiles 406, metal carbide powder are loaded, and through which meltedbraze enters the cavity, once the mold is heated, to infiltrate thevoids formed by the matrix of powder and tiles. The funnel is formedbetween two walls. An integrally formed circular extension 510 of themandrel forms an inner wall of the funnel 506. An outer wall of thefunnel is formed by extension 512 of the mold 500. Extension 510 of themandrel is removed during the finishing step 126 of process 100 (FIG.1).

FIGS. 6A-6C illustrate a second example of an inner radial bearing 600that is made using the mold and mandrel shown in FIGS. 7A and 7B. Theouter diameter of cylindrical bearing support 602 is clad with wearlayer 604 made with process 100 (FIG. 1). Microwave sintered metalcarbide tiles 606 form part of the wear layer matrix, along withspherical metal carbide, which surrounds the tiles. Unlike the innerradial bearing 400 of FIGS. 4A-4C, bearing 600 has lips 608 and 610extending over each end of wear layer 604. FIGS. 7A-7B illustrate anexample of mandrel 700, a section of which will form the cylindricalbearing support 602, as indicated in FIG. 7B, and a cooperating mold702. When mold 702 is press fitted to mandrel 700, the mandrel and moldcooperate to define a cylindrically shaped cavity between the mold andthe mandrel, into which microwave sintered metal carbide tiles 606 andmetal carbide powder are loaded through slot 704. A funnel 706 is formedabove the slot for facilitating loading of the tiles and powder, and forholding braze that will be infiltrated into the matrix of powder andtiles in the cavity when heated. Unlike funnel 506 (FIGS. 5A-5C), part708 is placed on top of the mandrel to cooperate with the mold to formthe funnel 706. An integrally formed circular section 709 of part 708forms an inner wall of the funnel 706. An outer wall of the funnel isformed by extension 710 of the mold 702. Part 708 is removed during thefinishing step 126 of process 100 (FIG. 1).

FIGS. 8A-C illustrate one example 800 of an outer bearing made using themold and mandrel of FIGS. 9A-C. Outer bearing 800 is substantially thesame as outer bearing 206 of FIG. 2, and can be used with the innerbearing shown in FIGS. 4A-4C in the manner shown in FIG. 2. The innerdiameter of cylindrical bearing support 802 is clad with wear layer 804made with process 100 (FIG. 1). Microwave sintered metal carbide tiles806 form part of the wear layer matrix, along with spherical metalcarbide, which surrounds the tiles. The cylindrical support 802 is madefrom a section of mandrel 902, as indicated in FIG. 9C. When mold 900 ispress fitted to mandrel 902, as shown in FIGS. 9A-9C, the mandrel andmold cooperate to define a cylindrically shaped cavity 904 between theouter diameter wall of mold 900 and the section of the mandrel that willform cylindrical support 802 of the bearing, as well a circular funnel906 that feeds into circular slot 908. The circular slot is an openinginto the top of cavity 902, through which tiles 806, metal carbidepowder are loaded, and through which melted braze enters the cavity,once the mold is heated, to infiltrate the voids formed by the matrix ofpowder and tiles. The funnel is formed between two walls. An integrallyformed circular extension 910 of the mandrel forms an outer wall of thefunnel 906. An inner wall of the funnel is formed by extension 912 ofthe mold 900. Extension 910 of the mandrel is removed during thefinishing step 126 of process 100 (FIG. 1).

FIGS. 10A-10C illustrate a second example 1000 of an outer bearing madeusing the mold and mandrel assembly shown in FIGS. 11A-11C. The outerdiameter of cylindrical bearing support 1002 is clad with wear layer1004 made with process 100 (FIG. 1). Microwave sintered metal carbidetiles 1006 form part of the wear layer matrix, along with sphericalmetal carbide. Unlike the outer radial bearing 800 of FIGS. 8A-8C,bearing 1000 has lips 1008 and 1010 extending over each end of wearlayer 1004. FIGS. 11A-1C illustrate an example of mandrel 700, a sectionof which will form the cylindrical bearing support 1002, as indicated inFIG. 11C, and a cooperating mold 702. When mold 1102 is press fitted tomandrel 1100, the mandrel and mold cooperate to define a cylindricallyshaped cavity between the mold and the mandrel, into which microwavesintered metal carbide tiles 1006 and spherical metal carbide powder areloaded through slot 1104. A funnel 1106 is formed above the slot forfacilitating loading of the tiles and powder, and for holding braze thatwill be infiltrated into the matrix of powder and tiles in the cavitywhen heated. Unlike funnel 906 (FIGS. 9A-9C), part 1108 is placed on topof the mandrel to cooperate with the mold to form the funnel 1106. Anintegrally formed circular section 1109 of part 1108 forms an inner wallof the funnel 1106. An outer wall of the funnel is formed by extension1110 of the mold 702. Part 1108 is removed during the finishing step 126of process 100 (FIG. 1). The finishing step includes removing part ofthe mandrel to arrive at the support 1002 as shown in FIGS. 10A-10C.

The foregoing description is of exemplary and preferred embodimentsemploying at least in part certain teachings of the invention. Theinvention, as defined by the appended claims, is not limited to thedescribed embodiments. Alterations and modifications to the disclosedembodiments may be made without departing from the invention. Themeaning of the terms used in this specification are, unless expresslystated otherwise, intended to have ordinary and customary meaning andare not intended to be limited to the details of the illustratedstructures or the disclosed embodiments.

1. A method of forming a wear layer on an article, the articlecomprising at least in part a steel support having a surface on whichthe wear layer is formed, comprising; arranging in a cavity formedbetween a mold and the surface of a support on which the wear layer willbe formed, an array of tiles made of microwave sintered metal carbidecomposite, wherein voids exist between each of the tiles in the array oftiles and immediately adjacent tiles, and between the each of the tilesin the array of tiles the mold and the surface of the support; fillingthe voids with metal carbide powder to form a matrix comprising thetiles and the spherical metal carbide powder; heating the brazing alloyto cause a brazing alloy to melt and infiltrate the matrix, heatingcomprising placing the mold containing the matrix, the bearing support,and unmelted brazing alloy with flux in an induction furnace andoperating the induction furnace for a period of time sufficient to allowthe brazing alloy to melt and uniformly infiltrate the matrix withoutdamaging the tiles; allowing the matrix to cool, thereby forming aconsolidation of the microwave sintered metal carbide tiles and theparticles of metal carbide on the bearing support, the consolidationcomprising the wear surface; and removing the mold and finishing thewear surface.
 2. The method of claim 1, wherein the microwave sinteredmetal carbide tiles are substantially uniform in shape and dimensionsover at least a portion of the wear surface.
 3. The method of claim 1,wherein the mold and support are made of steel.
 4. The method of claim1, wherein the mold with the matrix and support is heated for less thanan hour.
 5. The method of claim 1, wherein the mold with the matrix andsupport is heated to a temperature of approximately 1000 degrees Celsius(C) in an air atmosphere.
 6. The method of claim 1, wherein the tilesare comprised of microwave sintered tungsten carbide, cemented with acobalt alloy, and wherein the particles of metal carbide are comprisedof spherical tungsten carbide.
 7. The method of claim 1, wherein thesupport is part of a radial bearing.
 8. The method of claim 7, whereinthe support is part of a mandrel that cooperates with the mold to form afunnel into which brazing alloy is placed prior to heating.
 9. Themethod of claim 1, wherein the metal carbide powder is comprised ofparticles of metal carbide are of a spherical type and have a size of 25to 500 microns.
 10. The method of claim 9, wherein the metal carbide istungsten carbide.
 11. The method of claim 1, further comprising affixingat least one row of tiles to the surface of the mandrel support and thenassembling the support and the mold to form the cavity.
 12. The methodof claim 1, wherein the brazing alloy contains copper (Cu), nickel (Ni),and manganese (Mn).
 13. The method of claim 1, wherein each of tiles inthe array of tiles made of microwave sintered metal carbide compositehave a uniform size, shape and thickness.
 14. An article having at leastone wear surface, the article comprising a support with a surface and awear layer bonded to the surface, the wear layer functioning as the atleast one wear surface of the article and being comprised of aconsolidation, in brazing alloy, of a matrix comprised of a plurality ofmicrowave-sintered, metal carbide tiles in a closely spaced arrangementand metal carbide powder filling voids between the tiles, wherein thewear layer bonded to the steel support is a product of a processcomprising: arranging in a cavity formed between a mold and the surfaceof a support on which the wear layer will be formed, an array of tilesmade of microwave sintered metal carbide composite, wherein voids existbetween each of the tiles in the array of tiles and immediately adjacenttiles, and between the each of the tiles in the array of tiles the moldand the surface of the support; filling the voids with metal carbidepowder to form a matrix comprising the tiles and the spherical metalcarbide powder; heating the brazing alloy to cause a brazing alloy tomelt and infiltrate the matrix, heating comprising placing the moldcontaining the matrix, the support, and unmelted brazing alloy in aninduction furnace and operating the induction furnace for a period oftime sufficient to allow the brazing alloy to melt and uniformlyinfiltrate the matrix without damaging the tiles; allowing the matrix tocool, thereby forming a consolidation of the microwave-sintered metalcarbide tiles and the spherical particles of metal carbide on thesupport, the consolidation comprising the wear surface; and removing themold and finishing the wear surface.
 15. The article of claim 14,wherein the mold and the support are made of steel.
 16. The article ofclaim 14, wherein the mold with the matrix and support is heated forless than an hour.
 17. The article of claim 14, wherein the mold withthe matrix and steel support is heated to a temperature of approximately1000 degrees Celsius (C) in an air atmosphere.
 18. The article of claim14, wherein the metal carbide powder is spherical metal carbide powder.19. The article of claim 18, wherein the metal carbide is tungstencarbide.
 20. The article of claim 14, wherein the microwave-sinteredmetal carbide tiles are comprised of microwave-sintered tungsten carbidecemented with a cobalt alloy.
 21. The article of claim 14, wherein thebrazing alloy contains copper (Cu), nickel (Ni), and manganese (Mn). 22.The article of claim 14, wherein each of tiles in the array of tilesmade of microwave sintered metal carbide composite have a uniform size,shape and thickness.